Diagnostic Approach According to Uncovered Metastatic Sites: Mediastinum-Thymus, Peritoneum, Central Nervous System, and Soft Tissue

In metastases to the mediastinum, soft tissue, and central nervous system, lung and breast carcinomas occupy the front rows. Skin carcinomas should also be kept in mind in metastatic carcinomas of the soft tissue. The tumor type affects the selection of biomarkers to be applied to determine the primary focus. Notably, in a tumor with adenocarcinoma morphology, an immunohistochemical panel including general markers such as CK7 and CK20, as well as TTF-1 and Napsin-A for lung primary and GCDFP-15, GATA-3, ER, and PR for breast primary, would benefit to enlighten the majority of metastatic carcinomas seen in these regions. Almost half of the peritoneal metastases are composed of ovarian carcinomas, mostly serous carcinomas, and in the peritoneum, the most crucial point is to distinguish carcinoma metastases, especially serous carcinomas, from mesotheliomas. For distinction, an immunohistochemical panel including mesothelial markers such as calretinin and D2-40, a Müllerian marker such as PAX-8, ER, and epithelial markers such as Ber-EP4 and MOC-31 are useful. Additionally, homozygous deletion of BRCA1-associated protein 1(BAP-1) or p16 detected by FISH is specific for peritoneal mesotheliomas and can aid in the differential diagnosis.